Protective coating for planarization

ABSTRACT

Various pattern transfer and etching steps can be used to create features. Conventional photolithography steps can be used in combination with pitch-reduction techniques to form superimposed, pitch-reduced patterns of crossing elongate features that can be consolidated into a single layer. Planarizing techniques using a filler layer and a protective layer are disclosed. Portions of an integrated circuit having different heights can be etched to a common plane.

REFERENCE TO RELATED APPLICATIONS

This application is related to the following: U.S. patent applicationSer. No. 10/932,993 filed Sep. 1, 2004; U.S. patent application Ser. No.10/934,778 filed Sep. 2, 2004; U.S. patent application Ser. No.10/931,771 filed Aug. 31, 2004; U.S. patent application Ser. No.10/934,317 filed Sep. 2, 2004; and U.S. patent application Ser. No.11/134,982 filed May 23, 2005. Each of the above-listed references ishereby incorporated by reference in its entirety and made part of thisspecification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosed invention relates generally to integrated circuitfabrication, techniques for fabrication of computer memory, and maskingtechniques.

2. Description of the Related Art

As a consequence of many factors, including demand for increasedportability, computing power, memory capacity and energy efficiency inmodern electronics, integrated circuits are continuously being reducedin size. To facilitate this size reduction, research continues into waysof reducing the sizes of integrated circuits' constituent features.Examples of those constituent features include capacitors, electricalcontacts, interconnecting lines, and other electrical devices. The trendof decreasing feature size is evident, for example, in memory circuitsor devices such as dynamic random access memories (DRAMs), static randomaccess memories (SRAMs), ferroelectric (FE) memories,electronically-erasable programmable read-only memories (EEPROMs), flashmemories, etc.

Computer memory typically comprises millions of identical circuitelements, known as memory cells, arranged in a plurality of arrays withassociated logic circuitry. Each memory cell traditionally stores onebit of information, although multi-level cell devices can store morethan one bit per cell. In its most general form, a memory cell typicallyconsists of two electrical devices: a storage capacitor and an accessfield effect transistor. Each memory cell is an addressable locationthat can store one bit (binary digit) of data. A bit can be written to acell through the transistor and read by sensing charge on the storageelectrode from the reference electrode side. One common type of computermemory that can benefit from higher density components is DRAM. Bydecreasing the sizes of constituent electrical devices, the conductinglines that connect them, and the conductive contacts carrying chargebetween them, the sizes of the memory devices incorporating thesefeatures can be decreased. Storage capacities and circuit speed can beincreased by fitting more memory cells into the memory devices.

The demand for continual reduction in feature sizes places ever greaterdemands on techniques used to form the features. For example,photolithography is commonly used to pattern features on a substrate.The concept of pitch can be used to describe the size of these features.Pitch is the distance between identical points in two neighboringfeatures. These features are typically defined by spaces betweenadjacent features, which spaces may be filled by a material, such as aninsulator. As a result, pitch can be viewed as the sum of the width of afeature and of the width of the space separating that feature from aneighboring feature.

Certain photoresist materials only respond to certain wavelengths oflight. One common range of wavelengths that can be used lies in theultraviolet (UV) range. Because many photoresist materials respondselectively to particular wavelengths, photolithography techniques eachhave a minimum pitch below which that particular photolithographictechnique cannot reliably form features. This minimum pitch is oftendetermined by the wavelength of light that can be used with thattechnique. Thus, the minimum pitch of a photolithographic technique canlimit feature size reduction.

Pitch multiplication (or pitch doubling) can extend the capabilities ofphotolithographic techniques to allow creation of more densely arrangedfeatures. Such a method is illustrated in FIGS. 1A-1F and described inU.S. Pat. No. 5,328,810, issued to Lowrey et al., the entire disclosureof which is incorporated herein by reference and made part of thisspecification. For convenience, the method will also be briefly outlinedhere.

With reference to FIG. 1A, photolithography is first used to form apattern of lines 10 in a photoresist layer overlying a layer 20 of anexpendable material and a substrate 30. The layers shown in FIG. 1 areall shown schematically in cross-section. As shown in FIG. 1B, thepattern is then transferred by an etch step (preferably anisotropic) tothe layer 20, forming placeholders, or mandrels, 40. If the etch isanisotropic, the mandrels have approximately vertical sides, as shown.The photoresist lines 10 can be stripped and the mandrels 40 can beisotropically etched to increase the distance between neighboringmandrels 40, as shown in FIG. 1C. This isotropic etch (or shrink step)can alternatively be performed on the resist prior to transfer. A layer50 of spacer material is subsequently deposited over the mandrels 40, asshown in FIG. 1D. Spacers 60, i.e., material extending or originallyformed extending from sidewalls of another material, are then formed onthe sides of the mandrels 40 by preferentially etching the spacermaterial from the horizontal surfaces 70 and 80 in a directional (oranisotropic) spacer etch. Such spacers are shown in FIG. 1E. Theremaining mandrels 40 are then removed, leaving behind only the spacers60 above substrate 30. The spacers 60 together act as a mask forpatterning, as shown in FIG. 1F. Thus, where a given pitch formerlyincluded a pattern defining one feature and one space, the same widthnow includes two features and two spaces defined by the spacers 60. As aresult, the smallest feature size possible with a photolithographictechnique is effectively decreased by this “pitch-multiplication”technique.

While the pitch is actually halved in the example above, this reductionin pitch is conventionally referred to as pitch “doubling,” or, moregenerally, pitch “multiplication.” That is, conventionally“multiplication” of pitch by a certain factor actually involves reducingthe pitch by that factor. In fact, “pitch multiplication” increases thedensity of features by reducing pitch. Pitch thus has at least twomeanings: the linear spacing between identical features in a repeatingpattern; and the density or number of features per linear distance. Theconventional terminology is retained herein.

The critical dimension (CD) of a mask scheme or circuit design is thescheme's minimum feature dimension, or the measurement of the smallestwidth of the smallest feature that exists in that design or scheme. Dueto factors such as geometric complexity and different requirements forcritical dimensions in different parts of an integrated circuit,typically not all features of the integrated circuit will be pitchmultiplied. Furthermore, pitch multiplication entails many additionalsteps relative to conventional lithography; the additional steps caninvolve considerable additional expense. Pitch multiplication oftenprovides less control over the resulting features than that provided bydirect patterning without pitch multiplication, because the spacerpattern merely follows the outlines of the directly patterned features.Thus, pitch multiplication is typically thought useful only forregularly spaced lines, such as conductive lines for a memory array. Onthe other hand, typical micromasking techniques, such as isotropicshrink steps, can result in a reduction in feature size but nocorresponding increase in feature density. There have also beenchallenges in transferring very fine patterns to underlying layersbecause existing techniques do not adequately maintain resolution andfidelity through the transfer. There is a need for methods that canallow for smaller and more efficient operative units on an integratedcircuit; such methods will advantageously increase feature density anddecrease chip size.

Thus, there is a need for a reduction in the size of integrated circuitsand an increased operable density of the arrays of electrical devices oncomputer chips. Accordingly, a need exists for improved methods offorming small features; improved methods for increasing feature density;methods that will produce more efficient arrays; and techniques thatwill provide more compact arrays without harming feature resolution.

SUMMARY OF THE INVENTION

A method of planarizing a structure in a partially fabricated integratedcircuit is disclosed. The method can comprise providing elevatedfeatures in a first region, the elevated features having spaces amongthem. The method can also comprise depositing a filler layer over thefirst region and an adjacent second region. The method can also compriseproviding a protective layer over the filler layer, the protective layerbeing thinner over the first region compared to the second region.Furthermore, the method can comprise planarizing the filler layer afterproviding the protective layer.

In some embodiments, this application discloses a method of forming anarray for an integrated circuit. The method can include formingpitch-multiplied features separated by spaces in a first region. Themethod can further include introducing a filler layer that fills thespaces and covers the pitch-multiplied features in the first region andcovers the surface of a second region. The method can further includecoating the filler layer with a protective layer in both the first andsecond regions. Moreover, the method can include removing a portion ofthe protective layer in the first region and allowing a portion of theprotective layer to remain covering the filler layer in the secondregion. The method can include removing portions of filler layer throughplanarization of the first region while the filler layer is stillprotected by the protective layer in the second region. Furthermore, themethod can include removing the protective layer and planarizing thefirst and second regions to the same plane and forming a mask over atleast one of the first and second regions.

In some embodiments, a method of manufacturing computer memory isprovided. The method can comprise: forming separated features in amemory array region; depositing a filler layer around and over thefeatures in the memory array region and in a peripheral region such thatthe surface of the filler layer is less smooth than the surface of theperipheral region; forming a protective layer over the filler layer inboth the memory array region and the peripheral region; exposing thefiller layer under the protective layer in the array region beforeexposing the filler layer under the protective layer in the peripheralregion; and reducing the height of the features and filler layer in thememory array region to approximately the same height as the filler layerin the peripheral region.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A-1F are schematic, cross-sectional side views of mask lines,formed in accordance with a prior art pitch-multiplication method asdescribed above.

FIG. 2 is a schematic, cross-sectional side view of masking andsubstrate layers used to form an integrated circuit.

FIG. 3 shows the structure of FIG. 2 after photolithographic patterningof a first resist layer.

FIG. 4 shows the structure of FIG. 3 after an etch has reduced the sizeof the features in the pattern of FIG. 3.

FIG. 5 shows a schematic, cross-sectional side view of masking andsubstrate layers used to form an integrated circuit after the pattern ofFIG. 4 has been extended into underlying layers.

FIG. 6 shows the structure of FIG. 5 after overlying layers have beenstripped.

FIG. 7 shows the structure of FIG. 6 after blanket deposition of aspacer material.

FIG. 8 shows the structure of FIG. 7 after a spacer etch and subsequentetch, leaving a pattern of free-standing spacers that has been extendedinto an underlying layer.

FIG. 9 shows the structure of FIG. 8 after blanket deposition of afiller material.

FIG. 9.1 shows a cross-sectional view at the edge of an array offeatures similar to the structure of FIG. 8, after the spacers have beenremoved.

FIG. 9.2 shows the structure of FIG. 9.1 after blanket deposition of afiller material.

FIG. 9.3 shows the structure of FIG. 9.2 after deposition of aprotective layer.

FIG. 9.4 shows the structure of FIG. 9.3 after a selective etch hasremoved portions of the protective layer and filler material.

FIG. 9.5 illustrates the structure of FIG. 9.4 during the process ofanother selective etch, which has begun to remove some materials butwhile the protective layer is still functioning to protect some of thefiller material.

FIG. 9.6 illustrates the structure of FIG. 9.4 after selective etch ofFIG. 9.5 is completed, the protective layer has been completely removed,and planarization achieved.

FIGS. 9.7.2A-B show scanning electron micrographs (SEMs) of an exemplaryembodiment of a portion of the structure schematically depicted in FIG.9.2.

FIGS. 9.7.3A-9.7.3D show scanning electron micrographs (SEMs) of anexemplary embodiment of the structure schematically depicted in FIG.9.3.

FIGS. 9.7.6A-C show scanning electron micrographs (SEMs) of an exemplaryembodiment of the structure schematically depicted in FIG. 9.6, afterplanarization has occurred.

In FIGS. 10A-20D, the A figure (e.g., FIG. 10A) shows a schematic planview of the surface. The B figure (e.g., FIG. 10B) shows a schematic,cross-sectional side view taken along lines B-B (e.g., 10B-10B) of the Afigure (e.g., FIG. 10A). The C figure (e.g., FIG. 10C) shows aschematic, cross-sectional side view taken along lines C-C (e.g.,10C-10C) of the A figure (e.g., FIG. 3A). The D figure (e.g., FIG. 10D)shows a schematic, cross-sectional side view taken along lines D-D(e.g., 10D-10D) of the A figure (e.g., FIG. 10A). FIGS. 18E and 22E aresimilar to this pattern, showing a cross section taken along line E-E asindicated.

FIGS. 10A-10D show the structure of FIG. 9 after a CMP process or dryetch has removed the spacers and excess filler material.

FIGS. 11A-11D show the structure of FIG. 10 after deposition of multiplenew layers.

FIGS. 12A-12D show the structure of FIG. 11 after photolithographicpatterning of a second resist layer.

FIGS. 13A-13D show the structure of FIG. 12 after an etch has reducedthe size of the features in the pattern of FIG. 12.

FIGS. 14A-14D show the structure of FIG. 13 after the pattern of thefeatures of FIGS. 13A-13D has been extended into underlying layers topartially expose the crossing underlying pattern.

FIGS. 15A-15D show the structure of FIG. 14 after overlying layers havebeen stripped.

FIGS. 16A-16D show the structure of FIG. 15 after blanket deposition ofa spacer material.

FIGS. 17A-17D show the structure of FIG. 16 after a spacer etch andsubsequent etch (that has removed the mandrels), leaving a pattern offree-standing spacers that are orthogonal to the underlying pattern.

FIGS. 18-20 illustrate a process flow that can be used in conjunctionwith the structure of FIG. 17 to create a mask grid with small holesthat are densely spaced in an advantageous manner.

FIGS. 18A-18E show the structure of FIG. 17 after an etch (e.g., asilicon dioxide etch) has removed portions of several exposed layers,while leaving intact one of the stripe materials of exposed portions ofthe underlying pattern.

FIGS. 19A-19D show the structure of FIG. 18 after extending the patternof two overlying layers into an underlying mask or temporary layer,forming holes in the underlying layer. In the illustrated embodiment,the underlying temporary layer is amorphous carbon.

FIGS. 20A-20D show the structure of FIG. 19 after overlying layers havebeen stripped to leave a pattern of holes in the lower temporary or mask(e.g., amorphous carbon) layer.

FIG. 21A shows the structure of FIG. 20C after the pattern of holes inthe third temporary layer has been extended into the substrate, thethird temporary layer has been removed, and the holes have been filledwith conductive material.

FIG. 21B shows the structure of FIG. 21A after the overflow conductivematerial has been etched away.

FIGS. 22-25 illustrate a process flow that can be used in conjunctionwith the structure of FIG. 17 to create small mask pillars that aredensely packed in an advantageous manner.

FIGS. 22A-22E show the structure of FIG. 17 after an etch (e.g., anamorphous silicon etch) to remove one of the stripe materials of exposedportions of the underlying pattern.

FIGS. 23A-23B show the structure of FIG. 22 after a selective etch,(e.g., a silicon dioxide etch) has etched down portions of exposedmaterials in FIG. 22 to expose portions of an underlying mask ortemporary layer. In the illustrated embodiment, the underlying temporarylayer is amorphous carbon. The selective etch has not removed islands ofone of the stripe materials (e.g., silicon) that remain in place overthe temporary layer. FIG. 23A shows a schematic plan view of thesurface. FIG. 23B shows a schematic cross-sectional side view takenalong lines 23B-23B of FIG. 23A.

FIGS. 24A-24B show the structure of FIG. 23 after etching the exposedportions of the underlying temporary layer. The island pattern has thusbeen extended into the underlying material, leaving standing pillars orposts protected by silicon caps.

FIGS. 25A-25B show the structure of FIG. 24 after a silicon etch hasremoved the silicon caps from the pillars or posts. The pillars can beused as a mask for an underlying material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 2, a partially formed integrated circuit 100 isprovided. A substrate 110 is provided below various masking layers120-170. The layers 120-170 can be etched to form masks for patterningunderlying layers or substrate 110. These masks can be used to formvarious features, as discussed below. The features can comprise portionsof any of the following: one or multiple transistors, diodes,capacitors, conductive lines, gates, sources, drains, or contacts to anyof the above. These components can comprise portions of DRAM or flashmemory arrays, NOR logic arrays, NAND logic arrays, etc. In someembodiments, the features are formed from a substrate material thatcomprises a semi-conducting material. For example, the semi-conductingmaterial can be silicon, silicon-germanium compounds, or III-Vmaterials.

As used in this specification, the term “substrate” can refer not onlyto the substrate layer 110, but also to any layer that underlies anotherlayer. The term “substrate” can also describe a layer or layers thathave features or structures formed within them as a result of asemiconductor process (e.g., etching, doping, depositing, etc.)controlled by overlying masking layers.

As used in this specification, the term “pattern” can refer to an arrayor series of shapes that would be visible on a surface if viewed fromabove. A pattern can refer to the ensemble of shapes that correspond toa cross-section or shadow of features formed in one or multiple layers.The pattern is generally not the features themselves, but rather thedesign corresponding to the sizes and arrangement of the features. Apattern can be defined by a combination of patterns derived frommultiple overlying or side by side layers. A pattern can originate inone layer, such as a photodefinable layer, and then be transferred toanother layer, such as a temporary layer or a hard mask layer. Thepattern is said to be transferred to lower layers even if feature sizesand spacings are altered (e.g., by the feature shrink step noted above).In contrast, a new pattern can be defined by pitch multiplication,whereby two or more features in the second pattern replace one featureof the first pattern.

A pattern in one layer can be derived from one or more patterns inanother previous or overlying layer. A pattern can be said to be derivedfrom another pattern even if the features in the resulting layer do notexactly resemble those features which gave rise to the original pattern,but rather the underlying pattern generally follows the outline of theoverlying pattern with minor deviations in dimensions. The term “topattern” can also be used as a verb and means to create or form apattern.

An arrangement of features formed in a particular layer can give rise toa pattern. An array can also give rise to a pattern. An array is acollection of electrical components or features, formed in a repeatingconfiguration, that can span multiple layers of an integrated circuit.As described above, multiple cells can form a memory array for a DRAM orNAND flash memory circuit, for example, or a logic array.

The materials for the layers 120-170 overlying the substrate 110 arepreferably chosen based upon consideration of the chemistry and processconditions for the various pattern forming and pattern transferringsteps discussed herein. Because the layers between a topmost selectivelydefinable layer 120—which preferably is definable by a lithographicprocess—and the substrate 110 will preferably function to transfer apattern derived from the selectively definable layer 120 to thesubstrate 110, the layers between the selectively definable layer 120and the substrate 110 are preferably chosen so that they can beselectively etched relative to other exposed materials. A material isconsidered selectively, or preferentially, etched when the etch rate forthat material is at least about two times greater, preferably about tentimes greater and, most preferably, at least about forty times greaterthan that for surrounding materials.

In the illustrated embodiment of FIG. 2, the selectively definable layer120 overlies a first hard mask, or etch stop, layer 130, which overliesa first temporary layer 140, which overlies a second temporary layer150, which overlies a second hard mask, or etch stop, layer 160, whichoverlies a third temporary layer 170 to be processed (e.g., etched)through a mask, which overlies the substrate layer 110. In theillustrated embodiments, the third temporary layer 170 will serve as theultimate mask through which etching (or other processing) will beperformed. In some embodiments, amorphous carbon is a preferred materialfor the third temporary layer because so many other materials—silicon,silicon oxide, silicon nitride, etc.—can be selectively etched withoutsignificantly harming the carbon layer. For the illustrated embodiments,the substrate 110 may comprise an interlevel dielectric (ILD) layerthrough which contacts are to be formed.

In common methods of transferring patterns, both the mask and theunderlying substrate are exposed to an etchant, which preferentiallyetches away the substrate material. The etchants, however, can also wearaway the mask materials, albeit at a slower rate. Thus, over the courseof transferring a pattern, the mask can be worn away by the etchantbefore the pattern transfer is complete. These difficulties areexacerbated where the substrate 110 comprises multiple differentmaterials to be etched. In such cases, additional mask layers may beused to prevent the mask pattern from being worn away before the patterntransfer is complete. See FIGS. 9.1-9.7 for further illustration ofrelated masking processes.

Because the various layers are chosen based upon the requirements ofchemistry and process conditions, one or more of the layers can beomitted in some embodiments. In the illustrated embodiments, hard masklayers 130 and 160 advantageously play a protective role, protectingunderlying layers from unwanted degradation during etching of overlyinglayers. Similarly, for a particularly simple substrate 110, variousother layers, such as the second hard mask layer 160 itself, may beomitted and overlying mask layers may be sufficient for the desiredpattern transfer. Higher numbers of mask layers are advantageous fortransferring patterns to difficult to etch substrates, such as asubstrate comprising multiple materials or multiple layers of materials,or for forming small and high aspect ratio features.

With reference to FIG. 2, the selectively definable layer 120 ispreferably formed of a photoresist, including any photoresist known inthe art. For example, the photoresist can be any photoresist compatiblewith 13.7 nanometer (nm), 157 nm, 193 nm, 248 nm or 365 nm wavelengthsystems, 193 nm wavelength immersion systems or electron beamlithographic systems. Examples of preferred photoresist materialsinclude argon fluoride (ArF) sensitive photoresist, i.e., photoresistsuitable for use with an ArF light source, and krypton fluoride (KrF)sensitive photoresist, i.e., photoresist suitable for use with a KrFlight source. ArF photoresists are preferably used with photolithographysystems utilizing relatively short wavelength light, e.g., 193 nm. KrFphotoresists are preferably used with longer wavelength photolithographysystems, such as 248 nm systems. In other embodiments, the layer 120 andany subsequent resist layers can be formed of a resist that can bepatterned by nano-imprint lithography, e.g., by using a mold ormechanical force to pattern the resist.

Photoresist is typically patterned by being exposed to radiation througha reticle and then developed. In the case of negative photoresist,radiation, e.g., light, is focused on parts of the photoresist that areto be retained, e.g., on the areas where the lines—such as lines 124(see FIG. 3)—are to be formed. Typically, the radiation activates aphotosensitive compound, e.g., a photo-induced acid generator (PAG),which decreases the solubility of the photoresist, e.g., by causing itto polymerize. Preferred embodiments may be applied using any definablematerial, including positive or negative photoresist. A preferredreticle used in testing of some embodiments is T37Z 46/47 reticle.

The material for the first hard mask layer 130 preferably comprises aninorganic material, and exemplary materials include silicon dioxide(SiO₂), silicon, or a dielectric anti-reflective coating (DARC), such asa silicon-rich silicon oxynitride. In the illustrated embodiment, thefirst hard mask layer 130 is a dielectric anti-reflective coating(DARC). Thus, hard mask layer 130 can serve both as an intermediate hardmask and to reduce reflections during lithography. Using DARC materialfor the first hard mask layer 130 can be particularly advantageous forforming patterns having pitches near the resolution limits of aphotolithographic technique. The DARC can enhance resolution byminimizing light reflections, thus increasing the precision with whichphotolithography can define the edges of a pattern. Optionally, anorganic bottom anti-reflective coating (BARC) (not shown) can similarlybe used in addition to or in place of the first hard mask layer 130 tocontrol light reflections.

The first temporary layer 140 is preferably formed of amorphous carbon,which offers very high etch selectivity relative to the preferred hardmask materials. More preferably, the amorphous carbon is a form oftransparent carbon that is highly transparent to light and which offersfurther improvements for photo alignment by being transparent towavelengths of light used for such alignment. Deposition techniques forforming a highly transparent carbon can be found in A. Helmbold, D.Meissner, Thin Solid Films, 283 (1996) 196-203, the entire disclosure ofwhich is incorporated herein by reference and made part of thisspecification.

The second temporary layer 150 is preferably formed of amorphoussilicon. The benefits of using amorphous silicon will become apparent inthe context of the various etching and pattern transfer steps describedbelow. Amorphous silicon can be selectively etched while other adjacentmaterials (such as oxide layers) remain intact.

The second hard mask, or etch stop layer 160 preferably comprisessilicon dioxide (SiO₂), silicon, or a dielectric anti-reflective coating(DARC), such as a silicon-rich silicon oxynitride, or aluminum oxide(Al₂O₃). In the illustrated embodiment, the first hard mask layer 160 isa DARC.

The third temporary layer 170 is preferably formed of amorphous carbon,which has excellent etch selectivity relative to many materials.Benefits of amorphous carbon are further discussed above with respect tothe first temporary layer 140.

The substrate can be a silicon wafer used for formation of integratedcircuits. Various substrate materials can be used.

In addition to selecting appropriate materials for the various layers,the thicknesses of the layers 120-170 are preferably chosen dependingupon compatibility with the etch chemistries and process conditionsdescribed herein. For example, when transferring a pattern from anoverlying layer to an underlying layer by selectively etching theunderlying layer, materials from both layers are removed to some degree.Thus, the upper layer is preferably thick enough so that it is not wornaway over the course of the pattern transfer. The hard mask layers areadvantageously thin so that their transfer or removal can occur quickly,exposing surrounding materials to less wear.

In the illustrated embodiment, the selectively definable layer 120(e.g., photoresist) is a photodefinable layer preferably between about100-250 nm thick and, more preferably, between about 130-200 nm thick.The first hard mask layer 130 (e.g., SiO₂ or DARC) is preferably betweenabout 10-30 nm thick and, more preferably, between about 15-25 nm thick.The first temporary layer 140 (e.g., amorphous carbon) is preferablybetween about 100-200 nm thick and, more preferably, between about120-150 nm thick. The second temporary layer 150 (e.g., amorphoussilicon) is preferably between about 30-50 nm thick and, morepreferably, between about 35-45 nm thick. The second hard mask layer 160(e.g., SiO₂ or DARC) is preferably between about 10-30 nm thick and,more preferably, about 15 nm thick. The third temporary layer 170 (e.g.,amorphous carbon) is preferably between about 100-300 nm thick and, morepreferably, between about 150-250 nm thick.

The various layers discussed herein can be formed by various methodsknown to those of skill in the art. For example, various vapordeposition processes, such as chemical vapor deposition, can be used toform the various mask layers under the resist. Preferably, a lowtemperature chemical vapor deposition process is used to deposit thehard mask layers or any other materials, e.g., spacer material, overcarbon. Such low temperature deposition processes advantageously preventchemical or physical disruption of the underlying amorphous carbonlayer. Spin-on-coating processes can be used to form photodefinablelayers. In addition, amorphous carbon layers can be formed by chemicalvapor deposition using a hydrocarbon compound, or mixtures of suchcompounds, as carbon precursors. Exemplary precursors include propylene,propyne, propane, butane, butylene, butadiene and acetylene. A suitablemethod for forming amorphous carbon layers is described in U.S. Pat. No.6,573,030 B1, issued to Fairbairn et al. on Jun. 3, 2003, the entiredisclosure of which is incorporated herein by reference and made part ofthis specification. In addition, the amorphous carbon may be doped. Asuitable method for forming doped amorphous carbon is described in U.S.patent application Ser. No. 10/652,174 to Yin et al., the entiredisclosure of which is incorporated herein by reference and made part ofthis specification.

First Phase

In a first phase of methods in accordance with the preferred embodimentsand with reference to FIGS. 2-10, a pattern of spacers is formed bypitch multiplication and used to create an underlying striped structure(see FIG. 10) for subsequent method steps. One example of an etchsequence for this phase is the following: 1) deposition of multiplelayers; 2) photolithographic patterning of a first layer; 3) shrinkingof features; 4) extension of pattern into underlying layers; 5) removalof remaining portions of overlying layers; 6) blanket deposition ofspacer material; 7) spacer etch; 8) removal of spacer mandrels; 9)extension of spacer pattern into underlying material; 10) blanketdeposition of a filler material; 11) removal of spacers; and 12)planarization using protective masking techniques.

With reference to FIG. 3, a pattern comprising gaps or spaces 122delimited by definable material features 124 is formed in the definablelayer 120. The spaces 122 can be formed by, e.g., photolithography, inwhich the selectively definable layer 120 is exposed to radiationthrough a reticle and then developed. After being developed, theremaining definable material, photoresist in the illustrated embodiment,forms mask features such as the illustrated lines 124 (shown incross-section).

The pitch of the lines 124 is equal to the sum of the width of a line124 and the width of a neighboring space 122. To minimize the criticaldimensions of features formed using this pattern of lines 124 and spaces122, the pitch is preferably at or near the limits of thephotolithographic technique used to pattern the definable layer 120. Forexample, for photolithography utilizing 248 nm light, the pitch of thelines 124 can be about 200 nm. Thus, the pitch may be at the minimumpitch of the photolithographic technique and the spacer patterndiscussed below can advantageously have a pitch below the minimum pitchof the photolithographic technique.

As illustrated by FIG. 3, a preliminary step can comprise creating aseries of photoresist lines 124. Thus, photolithography can be used toform a plurality of lines in a mask material. Conventionalphotolithography can form lines having a pitch no smaller than thatdefinable by photons. However, subsequent pitch multiplication can formlines having a pitch that is smaller than that definable by conventionalphotolithography.

FIG. 4 shows the structure of FIG. 3 after the lines 124 have beenshrunk by an isotropic etch to create modified lines 124 a. The spaces122 can optionally be widened or narrowed to a desired dimension. Forexample, as illustrated in FIG. 6, the spaces 122 have been widened byetching the photoresist lines 124, to form modified spaces 122 a andmodified lines 124 a. The photoresist lines 124 are preferably reducedin size using an isotropic etch, such as a sulfur oxide plasma, e.g., aplasma comprising SO₂, O₂, N₂ and Ar, or any other suitable plasma. Twoother plasmas that can be used, for example, are an HBr/O₂ plasma or aCl₂/O₂ plasma. The isotropic etch degrades the exposed surfaces from alldirections. Thus, the corners of lines 124 a have been depicted asslightly rounded in FIG. 4. The extent of the etch is preferablyselected so that the widths of the lines 124 a are substantially equalto the desired spacing between the later-formed spacers 182, as will beappreciated from the discussion of FIGS. 7-8. Advantageously, this etchallows the lines 124 a to be narrower than would otherwise be possibleusing the photolithographic technique used to pattern the photodefinablelayer 120. That is, if the lines 124 are at or near the resolution limitof the photolithographic technique, this etch can reduce their size evenfurther, taking them below that resolution limit. In addition, the etchcan smooth the edges of the lines 124 a, thus improving the uniformityof those lines.

In some embodiments, the spaces 122 a between the lines 124 a can benarrowed by expanding the lines 124 to a desired size. For example,additional material (not shown) can be deposited over the lines 124, orthe lines 124 can be chemically reacted to form a material (not shown)having a larger volume to increase their size.

In the illustrated embodiment, the modified lines 124 a define thedimensions of placeholders or mandrels along which a pattern of spacers182 (FIG. 8) will be formed after transfer of the pattern to anunderlying layer (FIGS. 5 and 6) and blanket deposition of a spacermaterial 180 (FIG. 7). In alternative embodiments, if the deposition andetch of spacer material is compatible with the definable layer 120, thetemporary layer 140 can be omitted and the spacer material can bedeposited directly on the photo-defined lines 124 or the thinner lines124 a.

In other alternative embodiments, the pattern of the lines 124 can betransferred to underlying layers without first being trimmed or havingtheir width's reduced as described above. In such embodiments, a patterncorresponding to that of lines 124 can be formed in the temporary layer140 and the features of that pattern can be reduced in width with ashrink step.

As shown in FIG. 5, after modification of line width (FIG. 4), thepattern in the photodefinable layer 120 is preferably transferred to thefirst temporary layer 140 to allow for later deposition of a layer 180of spacer material (FIG. 7). The temporary layer 140 is preferablyformed of a material that can withstand the process conditions forspacer material deposition and etch, discussed below. In particular, thematerial forming the temporary layer 140 preferably has a higher heatresistance than photoresist and is preferably selected such that it canbe selectively removed relative to the material for the spacers 182(FIG. 8) and the underlying layer 150. As noted above, the layer 140 ispreferably formed of amorphous carbon.

As shown in FIG. 5, the pattern of lines 124 a and spaces 122 a in FIG.4 can be extended into, or transferred to underlying layers. Thispattern extension can be accomplished by selectively etching thematerials that form layers 130 and 140, while lines 124 a form aprotective mask that prevents the etchant from removing the materiallocated underneath lines 124 a.

To transfer the pattern into the hard mask layer 130, an anisotropicetch can be used, such as an etch using a fluorocarbon plasma. A wet(isotropic) etch may also be suitable if the hard mask layer 130 isthin. Preferred fluorocarbon plasma etch chemistries include CF₄, CFH₃,CF₂H₂ and CF₃H for etching the preferred DARC material.

To transfer the pattern into the first temporary layer 140, anSO₂-containing plasma, e.g., a plasma containing SO₂, O₂ and Ar, ispreferably used. Advantageously, the SO₂-containing plasma can etchcarbon of the preferred temporary layer 140 at a rate greater than 20times and, more preferably, greater than 40 times the rate that the hardmask layer 130 is etched. A suitable SO₂-containing plasma is describedin U.S. patent application Ser. No. 10/931,772 to Abatchev et al., filedAug. 31, 2004, entitled Critical Dimension Control, (Atty. docket No.MICRON.286A; Micron Ref. No. 2003-1348), the entire disclosure of whichis incorporated herein by reference and made part of this specification.Although FIG. 5 shows lines 124 a intact after the pattern has beenextended into the first temporary layer 140, the SO₂-containing plasmacan simultaneously etch the temporary layer 140 and also remove theremaining portion of definable layer 120.

As shown in FIG. 6, once the line pattern originally formed in the layer120 has been extended down into the layer 140, the remaining portions ofthe layer 120 can be stripped away using a selective etch.Alternatively, as noted above, the remaining portions of 120 can beetched away during an amorphous carbon etch step such as the step thatextends the pattern down into the layer 140. Thus, the line patternoriginally formed in the definable layer 120 has been transferred to thehard mask and temporary layers 130 and 140. The transferred pattern isapproximately the same as the line pattern originally formed in layer120; the transferred pattern has lines 144 a and spaces 142 a thatgenerally correspond to lines 124 a and spaces 122 a, respectively. Inthe illustrated embodiment, portions of the hard mask layer 130 remainin place as protective caps on the lines 144 a. These portions of thelayer 130 can act as etch stops in subsequent steps.

In the illustrated embodiment, a pattern is formed in an overlying layerand later transferred to an underlying layer. In FIG. 5, the illustratedwalls of the features formed in layers 130 and 140 are vertical, wherethese layers have been etched. In order to achieve vertical sidewalls inthis step and in other steps described herein, directional oranisotropic etches can be used.

Variations in etching processes can alter the precision with which apattern in an overlying layer corresponds to a pattern created in anunderlying layer. Although pattern transfer from layer to layer isgenerally illustrated schematically to be a precise process, withvertical walls, such precision may be difficult to achieve in practice.Thus, pattern transfer is intended to encompass general correspondencebetween underlying and overlying patterns. Similarly, pattern transferis meant to encompass modification of the features originally definingthe pattern—for example by enlarging or shrinking those features—wheresuch modification does not change the pitch.

As shown in FIG. 7, a layer 180 of spacer material is preferably blanketdeposited so that it conforms to the exposed surfaces, including thesecond temporary layer 150 and the lines 144 a. As shown, portions ofthe hard mask layer 130 can be left in place—to subsequently act as CMPetch stops—on top of lines 144 a when the layer 180 of spacer materialis deposited. Alternatively, the hard mask portions can be removed witha selective etch before spacer deposition. The spacer material can beany material that can act as a mask for transferring a pattern tounderlying layers, or that otherwise can allow processing of underlyingstructures through the mask being formed. The spacer materialpreferably: 1) can be deposited with good step coverage; 2) can bedeposited at a temperature compatible with the temporary layer 140 andunderlying layers; and 3) can be selectively etched relative to thetemporary layer 140 and any layer directly underlying the temporarylayer 140. Preferred materials include silicon oxides and nitrides. Thespacer material is preferably deposited by chemical vapor deposition oratomic layer deposition. The layer 180 is preferably deposited to athickness of between about 20-60 nm and, more preferably, about 20-50nm. Preferably, the step coverage is about 80% or greater and, morepreferably, about 90% or greater.

FIG. 8 shows the structure of FIG. 7 after a spacer etch and subsequentetch, leaving a pattern of free-standing spacers that has been extendedinto an underlying layer. The spacer etch can comprise an anisotropicetch to remove spacer material from horizontal surfaces. The spacer etchcan be performed using a fluorocarbon plasma. The spacer etch can alsobe performed using HBr/Cl plasma for a silicon spacer material. (Notethat preferred embodiments use silicon oxide spacers, however). After aspacer etch is performed, it can leave behind a pattern of elongatespacers having effectively reduced pitch relative to the lines.

After the spacer etch, the remaining portions of hard mask layer 130 (ifstill present) and the temporary layer 140 are next removed to leavefreestanding spacers 182. The remaining portions (in the form of lines144 a) of the first temporary layer 140 are selectively removed,preferably using a sulfur-containing plasma etch such as an etch usingSO₂. In this way, features of one pattern are removed to leave behindanother pattern formed by the spacers.

Thus, in some embodiments, pitch-reduction has been performed using aspacer material to create masking features. The masking features formedin this way can have a smaller pitch than the photoresist lines and cancomprise pitch-reduced masking lines separated by pitch-reduced spaces;pitch multiplication has been accomplished. In the illustratedembodiment, the pitch of the pattern formed by spacers 182 is roughlyhalf that of the pattern formed by photoresist lines 124 a and spaces122 a (FIGS. 3-5), where the pitch was originally determined byphotolithography. Preferably, a spacer pattern having a pitch of about100 nm can be formed.

With further reference to FIG. 8, the pattern formed by the spacers 182can be extended into the underlying second temporary layer 150. Theextension can be accomplished with a selective etch chemistry. Forexample, if the spacers 182 are formed from silicon dioxide and theunderlying layer 150 is formed from amorphous silicon, an etch canremove the latter while leaving the former largely intact. A preferredetch includes a physical component and preferably can also include achemical component and can be, e.g., a reactive ion etch (RIE), such asan HBr/Cl₂ etch. Such an etch can be performed, for example, using a LAMTCP9400 (available commercially from LAM Research Corporation ofFremont, Calif.) flowing about 0-50 sccm Cl₂ and about 0-200 sccm HBr atabout 7-60 mTorr pressure with about 300-1000 W top power and about50-250 W bottom power.

FIG. 9 shows the structure of FIG. 8 after blanket deposition of afiller material 190. The filler material 190 is advantageously formedfrom silicon dioxide (SiO₂). In some preferred embodiments, the spacers182 and the filler material 190 are formed from the same or similarmaterials, as will be better understood from the discussion of FIGS.17-20, and 22-23 below. Thus, the spacers 182 and the filler material190 can both be formed from silicon dioxide. One preferred process fordepositing the filler material 190 (i.e., silicon dioxide) is AppliedMaterials' Producer® HARP™ system. (HARP stands for “High Aspect RatioProcess.”)

In an alternative embodiment, the spacers 182 can be removed before thefiller material 190 is deposited. A wet etch can be used to remove thespacers if the hard mask layer 160 is formed from a DARC material.Removal of the spacers 182 can allow good coverage by the fillermaterial 190.

After the steps described above creating the structure depicted in FIG.9, some embodiments comprise a planarization step. However, at the edgeof the array, planarization of two different regions with differentheights can be difficult. For example, etch processes tend to planarizeuneven surfaces simultaneously. That is, two surfaces of differentheights will both be worn down by an etch, not just the higher surface.

FIGS. 8-9 show cross sections of the structure formed in the middle ofthe array of patterned features. The edge of the array is schematicallydepicted in FIGS. 9.1-9.6, which illustrate a planarization process thatuses a protective layer.

FIG. 9.1 shows the edge of the array at a similar point in the processas depicted in FIG. 8, (after the pattern formed by the spacers 182 isextended into the underlying second temporary layer 150), except thatthe spacers 182 have been removed. In some alternative embodiments, thespacers are not removed and subsequent steps can be performed with thespacers 182 in place, until they are removed during planarization.

FIG. 9.2 shows the structure of FIG. 9.1 after blanket deposition of afiller material 190. The filler material has a slightly non-planar,undulating surface in a higher region 912 with hills that roughlyoverlie the features (remaining portions of the temporary layer 150) andvalleys that roughly overlie the spaces between the features. The higherregion 912 can have underlying features that have been pitch-multiplied,causing the features to be tightly crowded together with relativelysmall spaces in between. The features can be spacers 182 or theremaining portions of the temporary layer 150. If the features are pitchmultiplied, the valleys overlying the spaces between features aregenerally less deep and, for some purposes, the higher region 912 (withthe filler material 190 deposited thereon) can be effectively treated asa monolithic higher region 912 rather than a series of discretefeatures.

To achieve a planarized surface at the level of the remaining portion ofthe second temporary layer 150 (as depicted in FIGS. 10A-10D), variousetch processes, including dry etch-back processes and chemicalmechanical planarization (CMP) processes can be used. Some etchprocesses involve only chemical etching or ion bombardment; CMPprocesses include both a chemical aspect and a mechanical aspect, eachof which contributes to removing some of the surface material. Themechanical aspect of a CMP process can be rotating pads that physicallywear down a surface like a rotating sander. However, these processestend to planarize uneven surfaces simultaneously. That is, two surfacesof difference heights will both be worn down by an etch, not just thehigher surface. The chemicals tend to wear down lower and highersurfaces simultaneously, causing two surfaces that have differentheights to still have different relative heights after etching. In thecase of CMP processes, the rotating pads of a CMP device do not presenta perfectly planar surface for contacting and wearing down the surfaceto be planarized. Increasing the speed of rotation of the pads used inthe CMP process does not protect the lower surface. Thus, if the surfacestarts out uneven (having more than one height) before CMP, it willlikely be uneven after CMP. Such an uneven surface is illustrated inFIG. 9.2, where the higher region 912 overlies the array of features,and the lower region 914 is located to the side of the array of features(e.g., in the periphery or logic region of a memory integrated circuit).

One approach to resolving the uneven planarization of such surfaces ofdifferent original heights was to “over-polish” or continue a CMPprocess past the original level of the lower region 914. This requiredthicker layers and wasted materials. Thus, it has been difficult toplanarize a selected portion to a selected level without causingunwanted change in the height of the other portion. An improved approachis described here, which uses a protective layer to improve theplanarization process at the edge of an array where the originalstructure has a higher region and a lower region.

FIG. 9.3 shows the structure of FIG. 9.2 after blanket deposition of aprotective layer 920. In some embodiments, the protective layer 920 isthinner where it overlies the higher region 912 and thicker where itoverlies the lower region 914. The protective layer 920 can be a spin-onfilm (e.g. photoresist, BARC, organic under layer, or SOD). Preferablythe protective layer 920 is formed from a material for which an etchchemistry will selectively etch the filler material 190 more quicklythan the protective layer 920. The thickness of the protective layer 920over the higher region 912 and lower region 914 can be determined by theviscosity of the protective layer 920, by the roughness or flatness ofthe underlying surface, and by the method of deposition. Spin-on coatingcan cause the undulating higher region 912 to have a thinner protectivelayer 920 than the lower, flatter region 914, as shown. For example, thethickness of the protective layer 920 in the higher region 912 can beapproximately 24 nm, while the thickness of the protective layer 920 inthe lower region 914 can be approximately 63 nm.

In some embodiments, the higher region 912 is less rough and undulatingthan that depicted in FIGS. 9.2 and 9.3. In some embodiments, thethinner coating of the protective material 920 on the higher region 912is due to the spin-on process, which generally tends to cause materialto flow to the lowest point on the structure. In some embodiments, theprotective layer 920 is thicker over the lower region 914 than thehigher region 912. In some embodiments, the protective layers over thehigher region 912 and the lower region 914 are approximately planar onthe top surface so that the two regions 912 and 914 have the same heightwhen the protective layer is applied.

FIG. 9.4 illustrates the structure of FIG. 9.3 after a first etch step.After the protective layer 920 has been deposited, a two-step etch canbe used to planarize the structure depicted in FIG. 9.3. A first etchstep can have a selectivity that etches the protective layer 920 morerapidly than the filler material 190. This step can remove the portionof the protective layer 920 that overlies the higher region 912, as wellas removing some of the filler material 190. This step can also removesome (but not all) of the protective layer 920 that overlies the lowerregion 914. If the protective layer 920 is photoresist and the fillermaterial 190 is oxide, a dry etch chemistry can be used for the firstetch step. In some embodiments, reactive ion etches and/or CMP processescan also be used.

FIG. 9.5 illustrates the structure of FIG. 9.4 at an intermediate timeduring the second etch step, after some materials have been removed butwhile the protective layer 920 is still functioning to protect thefiller material 190 in the lower region 914. A second etch step can havea selectivity that etches the filler material 190 more rapidly than theprotective layer 920 and that etches the filler material 190 atapproximately the same rate as the second temporary layer 150. After theprevious etch step has exposed the filler material 190 in the higherregion 912 (see FIG. 9.4), this second step can remove some of thefiller material 190, reducing the height of the higher region 912 withrespect to the lower region 914. The protective layer 920 can also bepartly removed during this step. If the protective layer 920 isphotoresist and the filler material 190 is oxide, a fluorocarbon etchcan be used for the second etch step.

FIG. 9.6 illustrates the structure of FIG. 9.4 after the second etchstep is completed, the protective layer 920 has been completely removed,and planarization achieved. As shown, the second etch step can continueuntil the protective layer 920 is completely removed. In someembodiments, the last part of the protective layer 920 is removed at thesame time that the higher region 912 and the lower region 914 have beenetched to approximately the same height. Thus, the array and the regionssurrounding the array have been planarized without having to over-etchand waste time and materials. If the second step continues slightlylonger, the second temporary layer 150 and the filler material 190preferably are etched at approximately the same rate so that the planarsurface is maintained. In some embodiments, the filler material 190 isthicker than the remaining portions of the temporary layer 150, so theprotective layer 920 is completely removed before any of the temporarylayer 150 is exposed. In this case, the etch can continue to remove theintervening filler material (which is inherently etched at a uniformrate because it is the same material both above the array features inwhat was formerly the higher region 912 and in the lower region 914). Insome embodiments, after the second etch step has reduced the higherregion 912 to roughly the same height as the lower region 914 using adry etch, for example, a separate (third) etch can be performed tofurther smooth or clean the planarized surface. The third etch step canbe a CMP process for example.

Various combinations of materials (such as those described above) can beused to form layers configured in the same way as those described here.Various etch chemistries can be used to selectively remove thosematerials.

FIGS. 9.7.2A and 9.7.2B show scanning electron micrographs (SEMs) of anexemplary embodiment of a portion of the structure schematicallydepicted in FIG. 9.2. The edge of the array is not visible in theseviews, which show only the higher region 912.

FIGS. 9.7.3A-9.7.3D show scanning electron micrographs (SEMs) of anexemplary embodiment of the structure schematically depicted in FIG.9.3. In these SEMs, the edge of the array is visible, showing thedifference in the thickness of the protective coat 920 in the higherregion 912 and the lower region 914.

FIGS. 9.7.6A, 9.7.6B and 9.7.6C show scanning electron micrographs(SEMs) of an exemplary embodiment of the structure schematicallydepicted in FIG. 9.6, after planarization has occurred.

The SEM's of FIGS. 9.7.2A-9.7.6C show structure that was formed using aLAM TCP9400 device with the following etch parameters:

Etch Step First Step Second Step Chamber Pressure (mTorr) 20 20 Flowrate of CF₄ (sccm) 75 n/a Flow rate of CH₂F₂ (sccm) n/a 45 Flow rate ofCF₄ (sccm) n/a 50 Flow rate of He (sccm) 75 100 Source Power (W) 600 800Bias Power (W) 90 75

As shown and described above, a protective coating can protect a lowersurface while a higher surface is exposed and etched by an etch process.If the higher surface wears down more slowly than the protective coatingand if sufficient topography is still remaining on the lower surface,the protective coating can be re-applied. If the etch has a mechanicalcomponent and the protective coating is thick enough, a surface that ishigher than the lower surface will be exposed first from the protectivecoating, so the higher surface will be etched for at least a short timewithout the lower surface being etched.

In some embodiments, two layers can be deposited: a first layer (e.g.,the filler material 190) that fills in the space in between the featuresof the array and a second layer (e.g., the protective layer 920) thatprotects portions of the first layer. The second layer smoothes over andfills in the depressions or shorter areas still present after depositionof the first layer. The second layer is a protective sacrificial layerbecause it is ultimately removed. The first layer is also partlyremoved, but portions of that layer remain interspersed with thefeatures of the array after planarization. In some embodiments, thepattern of the spacers 182 has not been extended or transferred into anunderlying layer, so the features of the array are the spacers 182themselves. In this case, the first layer can fill in the space betweenthe spacers 182.

The planarization processes disclosed herein can be used in a variety ofcircumstances, and not just in the context of the pitch-doubling andmasking steps described in detail herein. For example, the disclosedplanarization process can be used when a region having features (e.g., amemory array) is located next to a region without features (e.g., aperipheral or logic region). If the features are taller than the surfaceof the featureless region, their heights can be reduced using thetechniques discussed herein. In some embodiments, the planarizationprocess can be used where a higher surface having relatively non-smoothtopography is located next to a lower surface, allowing a protectivelayer to be thinner on the higher surface than on the lower surface.

FIGS. 10-20 and 22-23 each illustrate at least four corresponding views,lettered A-D as follows: 10A-10D, 11A-11D, etc. The views designatedwith an “A” consistently show a top or plan view, where hatching hasbeen included for convenience. The views B-C consistently show crosssections of the same structure depicted in the corresponding figure A.Furthermore, those views designated with a “B” consistently show thestructure in the same orientation as other views designated with a “B.”The orientations are also similar for “C” designations, and likewise for“D” designations.

FIGS. 10A-10D show the structure of FIG. 9 after removal of the spacers182 and a portion of the filler material 190, through, for example, achemical mechanical polishing (CMP) process. A dry etch or a plasma etchcan also be used for planarization. If a CMP process is used, a thinetch stop layer is preferably added between the hard mask layer 160 andthe temporary layer 150. The etch stop layer can be formed from Si₃N₄,for example.

FIG. 10A shows a schematic plan view of the surface after theplanarization. The surface exhibits a striped pattern with alternatingstripes of the filler material 212, which is amorphous silicon, forexample, and the stripes 214, which can be silicon dioxide, for example.The stripes 212 of amorphous silicon have been formed in the secondtemporary layer 150 and the stripes 214 of silicon dioxide are theremaining portions of the filler material 190 that fill the spacesbetween the stripes 212. For convenience, the surface in FIG. 10A isdepicted with cross-hatching to show the material that comprises thestriped structures. The stripes 212 preferably have widths 213 in arange of approximately 30-70 nm. The stripes 214 preferably have widths215 in a range of approximately 30-70 nm. More preferably, the stripes212 and 214 each have widths 213 and 215, respectively, of approximately50 nm. In the latter case, the pattern formed by the stripes has a pitchof approximately 100 nm.

FIG. 10B shows a schematic cross-sectional side view taken along lines10B-10B of FIG. 10A. This view reveals that the two sets of stripes areformed on the same “level.” For convenience in this application, theterm “level” is used to designate a portion of the integrated circuitthat is generally located in a thick plane that is parallel to andequidistant from the plane of the surface of the substrate 110. Thus,the layer 160 is located at a different level from that of layer 170,but the stripes 212 and the stripes 214 are located at the same level.In contrast, the term “layer” is generally used to refer to a portion ofthe integrated circuit formed from the same material and depositedtogether.

FIG. 10C shows a schematic, cross-sectional side view taken along lines10C-10C of FIG. 10B. FIG. 10D shows a schematic, cross-sectional sideview taken along lines 10D-10D of FIG. 10B.

In a first phase of methods described and illustrated above withreference to FIGS. 2-10, a pattern of spacers has been formed by pitchmultiplication and used to create an underlying striped structure or“first pattern” derived from and pitch multiplied relative to thepattern of the first resist mask.

Second Phase

In a second phase of methods in accordance with preferred embodimentsand with reference to FIGS. 11-17, a second pattern of spacers is formedby pitch multiplication and used to create an overlying stripedstructure (see FIG. 17) that crosses the underlying striped structure ofFIG. 10. One example of an etch sequence for this phase is thefollowing: 1) deposition of multiple layers; 2) photolithographicpatterning of an overlying layer; 3) shrinking of features; 4) extensionof pattern into underlying layers; 5) removal of remaining portions ofoverlying layers; 6) blanket deposition of spacer material; 7) spaceretch; 8) removal of spacer mandrels.

FIGS. 11A-11D show the structure of FIG. 10 after deposition of multiplenew masking layers, 320-340. The pattern having the stripes 212 and thestripes 214 now underlies multiple new layers of material. As with thelayers 120-170, layers 320-340 can also be etched to form masks forpatterning underlying layer(s) of substrate 110. These masks can be usedto form various features, as discussed below. The features can compriseportions of one or multiple integrated circuit components.

FIG. 11A shows a schematic plan view of the surface. FIG. 11B shows aschematic cross-sectional side view taken along lines 11B-11B of FIG.11A. FIG. 11C shows a schematic, cross-sectional side view taken alonglines 11C-11C of FIG. 11B. FIG. 11D shows a schematic, cross-sectionalside view taken along lines 11D-11D of FIG. 11B.

With reference to FIGS. 11A-11D, masking layer 320 preferably hassimilar properties to those described above with respect to layer 120.

With reference to FIGS. 11B-11D, layer 330 preferably has similarproperties to those described above with respect to layer 130.

With reference to FIGS. 11B-11D, the fourth temporary layer 340preferably has similar properties to those described above with respectto the layer 140.

As with the materials for the layers 120-170, the materials for layers320-340 overlying the substrate 110 are preferably chosen based uponconsideration of the chemistry and process conditions for the variouspattern forming and pattern transferring steps discussed herein. Suchlayers are also preferably chosen so that they can be selectively etchedrelative to other exposed materials.

In the illustrated embodiment of FIGS. 11A-11D, the second selectivelydefinable layer 320 overlies a third hard mask, or etch stop, layer 330,which overlies a fourth temporary layer 340, which overlies the levelhaving the stripes 212 and 214. Underlying levels 160 and 170, as wellas substrate 110, remain intact. As described above with respect to thelayers depicted in FIG. 2, one or more of the layers 320-340 can beomitted in some embodiments.

With reference to FIGS. 11A-11D, the second selectively definable layer320 is preferably formed of a photoresist, including any photoresistknown in the art. All the preferred properties and alternativesdescribed above with reference to the layer 120 also apply to the layer320.

The third hard mask layer 330 preferably comprises an inorganicmaterial, and in the illustrated embodiment, the layer 330 is a DARC.All the preferred properties and alternatives described above withreference to the layer 130 also apply to the layer 330.

The fourth temporary layer 340 is preferably formed of amorphous carbon.All the preferred properties and alternatives described above withreference to the layer 140 also apply to the layer 340. The layer 340 isformed from amorphous carbon in some embodiments. Because it is sometimedifficult to achieve good step coverage of amorphous carbon deposition,the underlying striped surface has been planarized (see FIG. 10).

As with the layers 120-170, the thicknesses of the layers 320-340 arepreferably chosen depending upon compatibility with the etch chemistriesand process conditions described herein. Thus, as described above,thicknesses must allow for appropriate pattern transfer, and the hardmask layer 330 is advantageously thin so that its transfer or removalcan occur quickly, exposing surrounding materials to less wear.

In the illustrated embodiment, the second selectively definable layer320 is a photodefinable layer preferably between about 100-250 nm thickand, more preferably, between about 130-200 nm thick. The third hardmask layer 330 is preferably between about 10-30 nm thick and, morepreferably, between about 15-25 nm thick. The fourth temporary layer 340is preferably between about 130-200 nm thick and, more preferably,between about 140-160 nm thick.

Furthermore, the layers 320, 330, and 340 can be formed by variousmethods known to those of skill in the art. For example, the methodsdescribed above for forming layers 120, 130, and 140 can be used to formlayers 320, 330, and 340, respectively.

FIGS. 12A-12D illustrate a pattern formed in the layer 320, having lines324 interspersed with spaces 322. The preferred properties of andmethods for forming the lines 124 described above in FIG. 3 et seq. alsoapply to lines 324, however, the lines 324 are not parallel to the lines124. This can be seen—even though the lines 124 have been removed—byobserving that the stripes 212 and the stripes 214 are not parallel tothe lines 324. Thus, because the stripes 212 and 214 are elongate in thesame elongate dimension of the lines 124, the lines 124 and the lines324 are not parallel.

Because the lines 324 are not parallel to the stripes 212 and 214, theillustrated method can be said to call for applying a crossing patternof photoresist over an underlying pattern. Thus, one pattern “crosses” asecond pattern when an elongate dimension of the first pattern is notaligned with or parallel to an elongate dimension of the second pattern.The elongate dimension of the lines 124 is aligned with the elongatedimension of the stripes 212 and 214, but the elongate dimension of thestripes 212 and 214 crosses the elongate dimension of the lines 324.Thus, the lines 124 can be described as aligned with the stripes 212 and214, and the stripes 212 and 214 can be described as crossing the lines324. In the illustrated embodiments, the lines 324 not only cross, theycross perpendicularly the stripes 212 and 214. However, the term “cross”is intended to include all non-parallel angles, not just a 90 degreeangle. Thus, though the exemplary features and/or holes formed by theillustrated methods have a generally rectangular footprint (see, e.g.,FIGS. 21A, 25A, and 27A), other footprints such as skewed quadrangle ordiamond-shaped footprints are also contemplated.

With reference to FIGS. 12A-12D, a pattern comprising spaces 322delimited by definable material features 324 is formed in the seconddefinable layer 320 in a similar way to what was described above withrespect to lines 124 and depicted in FIG. 3. Thus, FIGS. 12A-12D showthe structure of FIG. 11 after photolithographic patterning of anoverlying resist layer. FIG. 12A shows a schematic plan view of thesurface. FIG. 12B shows a schematic cross-sectional side view takenalong lines 12B-12B of FIG. 12A. FIG. 12C shows a schematic,cross-sectional side view taken along lines 12C-12C of FIG. 12B. FIG.12D shows a schematic, cross-sectional side view taken along the lines12D-12D of FIG. 12B.

As with the pattern depicted in FIG. 3, the pattern created by theseries of photoresist lines 324 has been formed through conventionalphotolithography. As with the earlier described pattern, the shrink stepcan be accomplished to make the lines 324 thinner and spacer formationcan be accomplished using the modified lines 324 a as mandrels, or thepattern can be transferred to an underlying layer before the shrink stepis accomplished. In the illustrated embodiment described below, however,the shrink step is performed on photoresist lines 324, the pattern isthen transferred to an underlying layer, and portions of the underlyinglayer form spacer mandrels.

FIGS. 13A-13D show the structure of FIG. 12 after the lines 324 havebeen shrunk, by an isotropic etch, for example, to create modified lines324 a. The shrink step also widens the spaces 322 to form modifiedspaces 322 a. FIG. 13A shows a schematic plan view of the surface. FIG.13B shows a schematic cross-sectional side view taken along lines13B-13B of FIG. 13A. FIG. 13C shows a schematic, cross-sectional sideview taken along lines 13C-13C of FIG. 13B. FIG. 13D shows a schematic,cross-sectional side view taken along lines 13D-13D of FIG. 13B.

The structure of FIGS. 13A-13D preferably shares many characteristics ofthe features described in conjunction with FIG. 4. Similar methods toachieve that structure can also be used; preferred etch materials andmethods, and desirable configurations are described above. For example,the photoresist lines 324 are preferably reduced in size using anisotropic etch, such as a sulfur oxide plasma, e.g., a plasma comprisingSO₂, O₂, N₂ and Ar, or any other suitable plasma. Two other plasmas thatcan be used, for example, are an HBr/O₂ plasma or a Cl₂/O₂ plasma.

As with the lines 124 a, the modified lines 324 a define the dimensionsof the placeholders or mandrels along which a pattern of spacers will beformed. The alternatives described above also apply here. For example,in alternative embodiments, the pattern of the lines 324 can betransferred to underlying layers without first being trimmed or havingtheir width's reduced as described above. In such embodiments, a patterncorresponding to that of lines 324 can be formed in the temporary layer340 and the features of that pattern can be reduced in width with ashrink step. In other alternative embodiments, if the deposition andetching of spacer material is compatible with the definable layer 320,the temporary layer 340 can be omitted and the spacer material can bedeposited directly on the photo-defined lines 324 or the thinner lines324 a.

In the illustrated embodiment, lines 324 a create a mask forplaceholders or mandrels that will later be formed in the underlyinglayer 340, along which a pattern of spacers 382 (FIG. 17) will be formedafter blanket deposition of a spacer material 380 (FIG. 16).

FIGS. 14A-14D illustrate how the pattern in the photodefinable layer 320can be extended into the fourth temporary layer 340. FIG. 14A shows aschematic plan view of the surface. FIG. 14B shows a schematiccross-sectional side view taken along lines 14B-14B of FIG. 14A. FIG.14C shows a schematic, cross-sectional side view taken along lines14C-14C of FIG. 14B. FIG. 14D shows a schematic, cross-sectional sideview taken along lines 14-14D of FIG. 14B.

The fourth temporary layer 340 preferably has the advantageousproperties described above for the second temporary layer 140 such ashigh heat resistance. As shown in FIGS. 14A-14D, the pattern of lines324 a and spaces 322 a in FIGS. 13A-13D can be extended into ortransferred to underlying layers in a similar way to the way the patternof lines 124 a and spaces 122 a was transferred to underlying layers,using, for example, a selective etch to transfer the pattern into thehard mask layer 330 and an SO₂-containing anisotropic plasma etch totransfer the pattern into the fourth temporary layer 340. Preferred andalternative etch chemistries are described above.

As illustrated in FIG. 14A, the described etch steps remove the portionsof the layers 330 and 340 that are not masked by the lines 324 a, thusleaving portions of the stripes 212 and 214 exposed. The surfacesvisible in FIG. 14A have been hatched to reveal the underlying materialsof the structure depicted, and to show how the lines 324 a cross thestripes 212 and 214.

FIGS. 15A-15D show the structure of FIG. 14 after the remaining portionsof the overlying layers 320 and 330 have been stripped. Such a processis described above and illustrated in FIGS. 5-6. FIG. 15A shows aschematic plan view of the surface. FIG. 15B shows a schematiccross-sectional side view taken along lines 15B-15B of FIG. 15A. FIG.15C shows a schematic, cross-sectional side view taken along lines15C-15C of FIG. 15B. FIG. 15D shows a schematic, cross-sectional sideview taken along lines 15D-15D of FIG. 15B. As illustrated by FIGS.15C-15D, lines 344 and spaces 342 exhibit the same crossing patternpreviously apparent in overlying layers (see lines 144 a and spaces 142a, for example).

As shown in FIG. 15, once the line pattern originally formed in thedefinable layer 320 has been extended down into the layer 340, theremaining portions of the definable layer 320 can be stripped away usinga selective etch. Alternatively, the remaining portions of layer 320 canbe etched away during the carbon etch step that extends the pattern downinto the layer 340. Thus, the line pattern originally formed in layer320 has been transferred to the layers 330 and 340. The transferredpattern is approximately the same as the line pattern originally formedin layer 320; the transferred pattern has lines 344 a and spaces 342 athat generally correspond to lines 324 a and spaces 322 a, respectively.In the illustrated embodiment, portions of the hard mask layer 330remain in place as protective caps on the lines 344 a. The lines 344 awill serve as mandrels for the subsequently formed spacers.

FIGS. 16A-16D show the structure of FIG. 15 after blanket deposition ofa spacer material 380 over the mandrels 344 a. FIG. 16A shows aschematic plan view of the surface. FIG. 16B shows a schematiccross-sectional side view taken along lines 16B-16B of FIG. 16A. FIG.16C shows a schematic, cross-sectional side view taken along lines16C-16C of FIG. 16B. FIG. 16D shows a schematic, cross-sectional sideview taken along lines 16D-16D of FIG. 16B.

The layer 380 of spacer material preferably resembles the layer 180 ofspacer material described above, in material, in thickness, in coverage,and in mode of deposition. In the illustrated embodiment, portions ofthe hard mask layer 330 have been left in place, although alternativeembodiments do not leave such portions in place. If the portions of thehard mask layer 330 are removed before spacer deposition, a selectiveetch can be used to remove them. Note that the material of the layer 380can be different from the materials of the layer 180, provided that eachlayer can be selectively etched with respect to other surrounding layersas described herein. Silicon dioxide is a preferred spacer material.

FIGS. 17A-17D show the structure of FIG. 16 after a spacer etch andsubsequent etch, leaving a pattern of free-standing spacers. FIG. 17Ashows a schematic plan view of the surface. FIG. 17B shows a schematiccross-sectional side view taken along lines 17B-17B of FIG. 17A. FIG.17C shows a schematic, cross-sectional side view taken along lines17C-17C of FIG. 17B. FIG. 17D shows a schematic, cross-sectional sideview taken along lines 17D-17D of FIG. 17B.

A preferred spacer etch and alternatives are described above withrespect to FIGS. 7-8. For example, the spacer etch can be performedusing fluorocarbon plasma. As with spacer etch described above, theresult is preferably a pattern of elongate spacers having effectivelyreduced pitch relative to the lines 344 a. After the spacer etch, theremaining portions of hard mask layer 330 (if still present) and thefourth temporary layer 340 are next removed to leave freestandingspacers 382. In this way, features of one pattern are removed to leavebehind another pattern formed by the spacers 382.

With the elongate spacers 382 in place, crossing the underlying masklines 212 and 214, a second pitch reduction process has been performedin a crossing dimension—that is, a dimension that is not parallel to thelines 212 and 214. In the illustrated embodiment, the pitch of thepattern formed by spacers 382 is roughly half that of the pattern formedby photoresist lines 344 and spaces 342. Advantageously, the pattern ofspacers 382 has a pitch of about 140 nm or less. Preferably, the patternof spacers 382 has a pitch of about 100 nm or less.

In a second phase of methods described and illustrated above withreference to FIGS. 11-17, a second pattern of spacers has been formed bypitch multiplication and used to create an overlying pattern of linesthat crosses the underlying pattern of lines illustrated in FIG. 10.

Third Phase

In a third phase of methods in accordance with preferred embodiments andwith reference to FIGS. 18-20, the crossing striped structures depictedin FIG. 17 are used to create a grid of material having small holes thatcan occur at regular intervals in two dimensions (see FIGS. 19-20). Oneexample of an etch sequence for this phase is the following: 1) removalof portions of several exposed layers made from a common material (suchas silicon dioxide), while leaving intact one of the materials (such asamorphous silicon) of exposed portions of the underlying stripematerials; 2) extension of two overlying patterns (such as an oxidespacer pattern and a crossing, amorphous silicon strip pattern) into anunderlying mask or temporary layer (such as amorphous carbon); and 3)removal of overlying layers to leave a single underlying layer havingholes.

FIGS. 18A-18E show the structure of FIG. 17 after exposed portions ofseveral layers, including the spacers 382 and the stripe 214, have beenselectively etched while the stripe 212 has been left largely intact. Ina preferred embodiment, the stripe 212 is formed from amorphous siliconand the spacers and the stripe 214 are formed from silicon dioxide, sothe etch is a silicon dioxide etch—that is, it etches silicon dioxideselectively with respect to the amorphous silicon that is also exposed.One etch that can be used is a fluorocarbon etch. FIG. 18A shows aschematic plan view of the surface. FIG. 18B shows a schematiccross-sectional side view taken along lines 18B-18B of FIG. 18A. FIG.18C shows a schematic, cross-sectional side view taken along lines18C-18C of FIGS. 18A and 18B. FIG. 18D shows a schematic,cross-sectional side view taken along lines 18D-18D of FIGS. 18A and18B. FIG. 18E shows a schematic, cross-sectional side view taken alongline 18E-18E of FIG. 18A.

FIGS. 19A-19D show the structure of FIG. 18 after an etch into exposedportions of the third temporary layer 170, which is preferably amorphouscarbon. FIG. 19A shows a schematic plan view of the surface. FIG. 19Bshows a schematic cross-sectional side view taken along lines 19B-19B ofFIG. 19A. FIG. 19C shows a schematic, cross-sectional side view takenalong lines 19C-19C of FIG. 19B. FIG. 19D shows a schematic,cross-sectional side view taken along lines 19D-19D of FIG. 19B.

FIGS. 20A-20D show the structure of FIG. 19 after overlying layers havebeen stripped to reveal the pattern of holes 412 in the third temporarylayer 170. FIG. 20A shows a schematic plan view of the surface. FIG. 20Bshows a schematic cross-sectional side view taken along lines 20B-20B ofFIG. 20A. FIG. 20C shows a schematic, cross-sectional side view takenalong lines 20C-20C of FIG. 20A. FIG. 20D shows a schematic,cross-sectional side view taken along lines 20D-20D of FIG. 20A.

FIG. 21A shows the structure of FIG. 20C after the pattern of holes 412in the third temporary layer 170 has been extended into the substrate110, the third temporary layer 170 has been removed, and the holes havebeen filled with a conductive material 420. The conductive material 420preferably substantially fills the holes in the substrate and overflowsto form a continuous overflow layer, as illustrated. The conductivematerial 420 can be any electrically conducting or semi-conductingmaterial. In a preferred embodiment, the conductive material 420 isdoped polysilicon. In some embodiments, the conductive material 420 canbe a conductive metal such as tungsten, copper, or aluminum. Theconductive material 420 often includes multiple sublayers. For example,a titanium adhesion layer, a metal nitride barrier layer, and a metalfiller layer can all be used in combination.

FIG. 21B shows the structure of FIG. 21A after the overflow conductivematerial has been etched. Preferably, the overflow material is removedusing a CMP process. In some embodiments, a hard mask layer (not shown)can be deposited between the third temporary layer 170 and the substrate110 to act as a CMP stop. Some embodiments can use an RIE or a sputteretch to remove the overflow material.

After the continuous overflow layer of conductive material 420 has beenremoved, portions of the conductive material form isolated contacts 422that are densely and/or regularly spaced. Preferred contacts have apitch width of less than 150 nm. More preferably, such contacts 422 havea pitch width of approximately 100 nm or less. In preferred embodiments,the illustrated substrate grid—that has been patterned from the carbongrid of the layer 170—provides insulation that separates the contacts422 from each other. In some embodiments the holes 412 can be used topattern or form other isolated features, such as posts for studcapacitors, trench capacitors, and/or posts for transistors.

In some embodiments, the holes can be used to pattern features formedfrom a semiconductor. These features can be formed by selective epitaxyin the mask holes, which can expose portions of a single-crystal siliconlayer below the mask layer. The features can comprise vertical surroundgate transistors that connect a source region (not shown) in anunderlying level to a drain that is part of the isolated feature. Thus,the hole can have within it, or the feature can act as, a channelconnecting a source region to a drain.

Once the carbon grid has been filled with conductive material, thecarbon grid of the modified layer 170 can be removed to leavefreestanding conductive contacts 422. The spaces between contacts canthen be filled with an insulating material such as oxide (not shown). Insome embodiments, the pattern of modified layer 170 is first extendedinto the substrate layer 110 (such as an ILD), and contacts are formedat the lower level.

In some embodiments, the holes 412—whether extended into the substrate110 or in an overlying layer—are configured to receive an electricallyconductive material such as metal. Furthermore, when used in formationof an integrated circuit, the holes 412 are preferably positioned toallow formation of an electrically conductive contact that connectsunderlying features such as transistor source regions with othercomponents (for example, bit lines) in an overlying level.

In a third phase of methods described and illustrated above withreference to FIGS. 18-21, the crossing striped structures depicted inFIG. 17 were used to create a grid of mask material having small,densely arranged holes that occur at regular intervals in twodimensions. The mask holes, or holes etched into an underlying layerthrough the mask, can then be filled with material to create small,densely spaced features in the grid, as depicted in FIG. 21. The skilledartisan will readily appreciate other applications for employing themask with a dense pattern of holes.

As illustrated in FIG. 17, masks with different patterns in distinctlayers can both shield the underlying layers or substrate. FIGS. 18-21show one way that the two patterns can operate together or beconsolidated to effectively form a combined pattern or mask from twosuperimposed patterns. Subsequent figures show further examples ofpattern consolidation, which can be especially beneficial when the twopatterns have crossing features or patterns.

Fourth Phase

In a fourth phase, alternative to the third phase of methods inaccordance with preferred embodiments and with reference to FIGS. 22-25,the crossing striped structures depicted in FIG. 17 are used to createsmall, densely arranged mask features (such as free-standing pillars orposts) that occur at regular intervals in two dimensions. In particular,FIGS. 17 and 22-25 show one approach to making such isolated maskfeatures.

FIGS. 22-25 illustrate a process flow that can be used in conjunctionwith the structure of FIG. 17 to create pillars that are small anddensely and/or evenly spaced in an advantageous manner. One example ofan etch sequence for this phase is the following: 1) removal of exposedportions of one of the stripe materials (such as amorphous silicon);while leaving intact the other exposed materials (such as silicondioxide); 2) removal of spacers, the other stripe material, and exposedportions of the hardmask layer (this can be accomplished in a singleetch step if all three are formed from the same material); and 3)extension of the resulting pattern (i.e., mask of amorphous siliconislands) into the underlying layer to form freestanding mask pillars orposts.

FIGS. 22A-22D show the structure of FIG. 17 after the exposed portionsof the stripes 212 have been removed, leaving a three-tiered surfaceexposed (portions of the spacers 382, the stripes 214, and the layer 160are all exposed). FIG. 22A shows a schematic plan view of the surface.FIG. 22B shows a schematic cross-sectional side view taken along lines22B-22B of FIG. 22A. FIG. 22C shows a schematic, cross-sectional sideview taken along lines 22C-22C of FIG. 22B. FIG. 22D shows a schematic,cross-sectional side view taken along lines 22D-22D of FIG. 22B.

An HBr/Cl₂ etch material can be used to selectively remove exposedportions of the stripes 212, if they are formed from amorphous silicon,for example.

FIG. 22A illustrates that in some embodiments, portions of threedifferent silicon oxide layers can be exposed; the spacers 382, thestripes 214, and the second hard mask layer 160 each can be formed fromsilicon dioxide. The materials of these separate layers have beendepicted using stipple of varying weights so that the three layers (160,214, and 382) can be distinguished in the drawings. In otherembodiments, the second hard mask layer 160 is formed from a DARCmaterial, as noted above.

FIGS. 23A-23B show the structure of FIG. 22 after a selective etch hasremoved all portions of the various oxide features depicted in FIG. 22Athat are not masked by the newly exposed islands or caps (formed, forexample, from amorphous silicon). This etch step exposes portions of anunderlying layer (formed, for example, from amorphous carbon). FIG. 23Ashows a schematic plan view of the surface. FIG. 23B shows a schematiccross-sectional side view taken along lines 23B-23B of FIG. 23A.

If each is formed from the same material, such as silicon dioxide in apreferred embodiment, the spacers 382, the remaining portions of thestripes 214, and the non-protected portions of the hard mask layer 160can all be removed in a single etch step. Alternatively, separate etchsteps can be used to remove each of these materials. For example, in oneetch step, the spacers 382 can be selectively removed relative to thematerial of the caps 432 that are formed from silicon, for example.Newly exposed portions of the stripes 214 can then be removed once thespacers 382 no longer protect those portions. Then portions of the hardmask layer that are not protected by the amorphous silicon islands orcaps 432 can be removed.

FIGS. 24A-24B show the structure of FIG. 23 after anisotropic etch stepshave extended the island pattern of FIG. 23 into an underlying layer,leaving standing pillars 430 protected by amorphous silicon caps 432.FIG. 24A shows a schematic plan view of the surface. FIG. 24B shows aschematic cross-sectional side view taken along lines 24B-24B of FIG.24A.

The etch steps have removed the portions of the third temporary layer170 (preferably formed from amorphous carbon) that is not masked by theamorphous silicon caps 432. The amorphous silicon caps 432 comprise theremaining portions of the stripes 212, which were formed from the secondtemporary layer 150. The caps 432 protect the column of material that islocated underneath the caps 432. Thus, the caps 432 form a pattern ofsmall, protective masking islands that can be densely and/orevenly-spaced, made possible by the overlying crossing patterns thathave defined the non-island portions of the structure. The caps 432 andthe resulting pillars 430 can be densely and/or evenly spaced. FIG. 24Bshows the pillars 430 in cross section, and reveals how the pillars aresurrounded by spaces 434 in each dimension that preferably extend allthe way down through the modified layer 170 to the layer 110. From thispoint, the pattern present in the modified layer 170 can be furtherextended into the substrate 110 by extending the spaces 434 down intothe substrate 110. That is, the modified layer 170 can be used as a maskto form pillars or islands in the substrate 110.

FIGS. 25A-25B show the structure of FIG. 24 after an amorphous siliconetch has removed the amorphous silicon caps 432 from the pillars 430 toform modified mask pillars 430 a. Alternatively, a CMP process can beused to remove the amorphous silicon caps 432.

In some embodiments, the pillars or posts are formed from asemiconducting material. Preferably, carbon pillars are used as a maskto etch silicon pillars in an underlying semiconducting substrate. In analternative embodiment, the carbon layer 170 can be omitted and theholes can be formed directly in the substrate 110, which can be asilicon wafer or a blanket epitaxial layer. As described above,semiconducting pillars can comprise vertical surround gate transistorsthat connect a source region in an underlying level to a drain in theupper portion of the pillar. Thus, the pillar or post can have withinit, or act as, a channel connecting a source region below to a drainabove.

In a fourth, alternative phase of methods in accordance with preferredembodiments and with reference to FIGS. 22-25, the crossing stripedstructures depicted in FIG. 17 have been used to create small, denselyarranged features that occur at regular intervals in two dimensions. Inparticular, FIGS. 17, and 22-25 have shown one approach to making suchfeatures.

An alternative way to form a grid structure similar to the grid formedin modified layer 170 a and illustrated in FIGS. 21A-21D is to form thepillars 430 illustrated in FIGS. 24 and 25, fill the spaces in betweenthe pillars 430 with a material selectively etchable with respect to theamorphous carbon of pillars 430, polish the material back to the top ofthe pillars 430, and use a selective etch to remove the pillars 430. Analternative way to form a pillar structure similar to the structureillustrated in FIGS. 24 and 25 is to form the modified layer 170 a, fillthe holes 412 with a material selectively etchable with respect to thethird temporary layer 170 a, polish the material back to the surface ofthe amorphous carbon layer 170 a, and use a selective etch to remove themodified layer 170 a. Using these positive and negative approaches inturn, while masking off adjacent portions of the array, pillars or postsand grids can be formed in adjacent portions of an array.

1. A method of planarizing a structure in a partially fabricatedintegrated circuit, the method comprising: providing elevated, pitchdoubled features in a first region, the elevated features having spacesamong them; depositing a filler layer over the first region and anadjacent second region; providing a protective layer over the fillerlayer, the protective layer being thinner over the first region comparedto the second region; and planarizing the filler layer after providingthe protective layer.
 2. The method of claim 1, wherein the elevatedfeatures are lines in a memory array.
 3. The method of claim 1, whereinthe filler layer fills the spaces among the features.
 4. The method ofclaim 3, wherein planarizing comprises exposing tops of the features andleaving the filler layer between the features and not over the features.5. The method of claim 1, wherein planarizing comprises chemical vapordeposition.
 6. The method of claim 1, wherein planarizing comprises dryetching.
 7. The method of claim 1, wherein the protective layer preventsremoval of the filler layer in the second region while planarizing thefiller layer in the first region.
 8. The method of claim 1, whereinplanarizing comprises removing the protective layer in the first regionbefore removing the protective layer in the second region.
 9. A methodof forming an array for an integrated circuit comprising: formingpitch-multiplied features separated by spaces in a first region;introducing a filler layer that fills the spaces and covers thepitch-multiplied features in the first region and covers the surface ofa second region; coating the filler layer with a protective layer inboth the first and second regions; removing a portion of the protectivelayer in the first region; allowing a portion of the protective layer toremain covering the filler layer in the second region; removing portionsof filler layer through planarization of the first region while thefiller layer is still protected by the protective layer in the secondregion; removing the protective layer and planarizing the first andsecond regions to the same plane; and forming a mask over at least oneof the first and second regions.
 10. The method of claim 9, furthercomprising planarizing the first region down to the top of thepitch-multiplied features so that the filler material formsdiscontinuous portions in between the pitch-multiplied features.
 11. Themethod of claim 9, wherein the mask is pitch multiplied.
 12. The methodof claim 9, wherein the pitch multiplied features are spacers.
 13. Themethod of claim 9, wherein the protective layer has poor step coverage.14. The method of claim 9, wherein the protective layer is a definablelayer.
 15. The method of claim 9, wherein the protective layer isphotoresist.
 16. The method of claim 9, wherein the filler layer isamorphous carbon.
 17. The method of claim 9, wherein the filler layer inthe first region has a surface with hills and valleys that are filled anplanarized by the protective layer.
 18. The method of claim 9, whereinthe filler layer has approximately the same maximum thickness over thepitch-multiplied features as it does in the second region.
 19. Themethod of claim 9, wherein the protective layer is thinner in the firstregion than it is in the second region.
 20. The method of claim 9,wherein the protective layer has a top surface that is approximately onthe same plane in both the first and second regions after beingdeposited over the filler layer.
 21. The method of claim 9, wherein theprotective material has a top surface that generally is higher in thefirst region than in the second region.
 22. The method of claim 9,wherein the protective layer is spun on.
 23. A method of manufacturingcomputer memory comprising: forming separated features in a memory arrayregion; depositing a filler layer around and over the features in thememory array region and in a peripheral region such that the surface ofthe filler layer is non-planar; forming a protective layer over thefiller layer in both the memory array region and the peripheral region;exposing the filler layer under the protective layer in the array regionbefore exposing the filler layer under the protective layer in theperipheral region; and reducing the height of the features and fillerlayer in the memory array region to approximately the same height as thefiller layer in the peripheral region.
 24. The method of claim 23,wherein the separated features comprise masking features.
 25. The methodof claim 23, wherein the surface of the filler layer is less smooth thanthe surface of the peripheral region prior to formation of theprotective layer.
 26. The method of claim 23, wherein the separatedfeatures comprise spacers.
 27. The method of claim 23, wherein theseparated features comprise lines of sacrificial material.
 28. Themethod of claim 27, wherein the lines of sacrificial material are pitchreduced.
 29. The method of claim 23, wherein the peripheral region is alogic region.
 30. The method of claim 23, wherein an upper surface ofthe peripheral region is lower than an upper surface of the memory arrayregion prior to depositing the filler layer.
 31. The method of claim 23,wherein forming a protective layer comprises applying a spin-on coat ofphotoresist.
 32. The method of claim 23, wherein the protective layer isgenerally thinner in the memory array region when it is formed than itis in the peripheral region.
 33. The method of claim 23, whereinexposing the filler layer under the protective layer in the array regionbefore exposing the filler layer in the periphery region is accomplishedby a selective etch.
 34. The method of claim 23, wherein exposing thefiller layer under the protective layer in the array region beforeexposing the filler layer in the periphery region is accomplished by atimed etch.
 35. The method of claim 23, wherein the protective layer inthe memory array region is removed before the protective layer isremoved in the peripheral region.
 36. The method of claim 23, whereinreducing feature heights comprises a chemical mechanical planarizationprocess.
 37. The method of claim 23, wherein reducing feature heightscomprises a dry etch process.
 38. The method of claim 23, whereinexposing the filler layer comprises first exposing portions of thefiller layer that are taller before exposing portions of the fillerlayer that are lower.
 39. The method of claim 23, wherein forming aprotective layer comprises forming a protective layer that is thinnerover taller portions of topography in the filler layer and thicker overshorter portions of the topography in the filler layer.